Vampire Trolls: Oddly enough, this happens rather often. Trolls are the only other race besides humans who are really susceptible to vampirsim.
Cave Trolls: Cave trolls usually can't control their thirst for blood and go on a killing rampage. Often running out of blood and dying before they can find more. Though Stone trolls can go up to eight days without blood.
They have many weaknesses, sunlight still turns them to stone, sliver and dragonbone do damage that doesn't allow regeneration to work. They do however gain lots of bonuses from it as well, regeneration, super strength, quickness and the ability to jump unnaturally high, cloaking themselves invisible for a minute or so.
Slender Trolls: Slender trolls who catch vampirism often live in lonely caves in the tundra areas. They hunt at night, feeding on anything it can get its hands on--even its own kind. Since Slender trolls can regenerate, its like a never ending supply of blood.
The regeneration factor of Slender trolls and those gained by vampirism, makes for an amazingly quick heal. A slash crossed the chest heals in seconds after being opened. But they also gain more weaknesses, Silver and Dragon bone cause a burning effect to the wound that cannot be regenerated. However they gain some powers as well, such as super strength, quick reflexes, and all their 5 senses and intuition are amplified. Also they can gain knowledge through blood like most vampires, teaching them things most trolls wouldn't know, making them dangerous opponents. For some reason Slender trolls can't turn into mist like most vampires, but they can cloak themselves invisible for a few minutes.
War Trolls: This has never happened as far as anyone knows.